Thank Me Later <= 3.3.4 - Admin+ Stored Cross-Site Scripting

The plugin does not sanitise and escape the Message Subject field before outputting it in the Messages list, which could allow high privileges users such as admin to perform Cross-Site Scripting attacks even when the unfiltered_html capability is disallowed

Add/Edit a message and put the following payload in the Subject field: "><img src onerror=prompt(/XSS/)>

The XSS will be triggered in the Messages list (/wp-admin/admin.php?page=bbpp_thankmelater)